Tropical Storm Norma Forecast Discussion Number 1

NOAA - Tropical Weather Updates

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Issued at 300 PM MDT Tue Oct 17 2023

WTPZ42 KNHC 172016
Tropical Storm Norma Discussion Number   1
NWS National Hurricane Center Miami FL       EP172023
300 PM MDT Tue Oct 17 2023
Satellite imagery this afternoon depicts that the area the National 
Hurricane Center has been monitoring offshore of the southwestern 
coast of Mexico (EP90) has become better organized. Showers and 
thunderstorms have been consolidating, with curved band features 
developing around a recently well-defined low-level center. 
Subjective Dvorak satellite intensity estimates are T2.5/T3.0 from 
TAFB and SAB, respectively. Given the improved satellite 
presentation and these intensity estimates, advisories are being 
initiated on Tropical Storm Norma with an initial intensity of 35 
Norma is in a fairly conducive environment for intensification. Low 
vertical wind shear, warm sea surface temperatures, and favorable 
upper-level diffluence will likely lead to steady to rapid 
strengthening for the next few days.  DTOPS and SHIPS rapid 
intensification (RI) indices are between 60 to 70 percent for a 55 
kt increase over the next 48 hours, and the NHC forecast is near 
that value, explicitly forecasting RI between 12 to 36 hours. 
Towards the end of the forecast, increasing vertical wind shear and 
potential drier air intrusions could cause the system to gradually 
weaken. The NHC forecast lies just below the HCCA HFIP corrected 
consensus aids, and it is noted that the HAFS-A/B hurricane regional 
models show a higher, but still plausible, peak intensity.
Norma is moving west-northwestward at an estimated motion of 285/9 
kt. The system is expected to turn more northwestward at a slightly 
slower forward speed during the next few days around the western 
periphery of a mid-level ridge. Towards the end of the forecast 
period as the system moves toward the Baja peninsula, there is a 
notable divergence among the model suite.  A stronger vortex, as 
depicted in the GFS/CMC model, would be picked up by an approaching 
trough from the northwest and move the system northeastward towards 
the Baja peninsula.  However, a weaker vortex would tend to meander 
south of the peninsula and be missed by the approaching trough, 
like the ECMWF/UKMET solutions.  Since the NHC intensity forecast 
is on the strong side of the guidance, the official track is closer 
to the right side of the guidance envelope, more similar to the GFS 
and HCCA models.
INIT  17/2100Z 13.2N 107.3W   35 KT  40 MPH
 12H  18/0600Z 13.8N 108.0W   45 KT  50 MPH
 24H  18/1800Z 15.0N 108.4W   60 KT  70 MPH
 36H  19/0600Z 16.0N 108.6W   75 KT  85 MPH
 48H  19/1800Z 16.9N 108.8W   85 KT 100 MPH
 60H  20/0600Z 17.8N 109.1W   95 KT 110 MPH
 72H  20/1800Z 18.7N 109.6W   95 KT 110 MPH
 96H  21/1800Z 20.9N 110.3W   90 KT 105 MPH
120H  22/1800Z 22.5N 110.0W   85 KT 100 MPH
Forecaster Kelly

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